There is known an apparatus for molding articles from fibrous concrete comprising a tray, and a working mechanism in the form of nozzles adapted to spray under pressure binders (such as cement or gypsum), aggregate, water, and fibres. All the ingredients are sprayed layer-by-layer onto the tray until obtaining a product of required thickness.
This prior art apparatus is difficult to manufacture. Another disadvantage is a rather low efficiency of the apparatus and insufficient strength of fibrous concrete products made thereby, since spraying calls for the use of excessive amounts of water, whereby the resulting product lacks the desired uniformity of fiber distribution, and is not homogeneous in terms of density. In addition, since the fibres fail to be sufficiently enveloped by the laitance, it is impossible to obtain products of uniform thickness.
There is also known an apparatus for molding concrete products comprising a hopper with a feeding means, a working member in the form of screw conveyer, and a compacting roller, all mounted in succession on a gantry. The screw conveyer is intended to smooth out the mix on the tray, and is arranged horizontally ahead of the roller (cf., U.S. Pat. No. 3,541,931; Int. Cl. E 01 C 19/22).
This apparatus is inherently disadvantageous because during molding thin-wall articles from fibrous concrete the screw conveyer fails to uniformly place the mix across the tray; the fibrous concrete mix tends to clot to affect the integrity of fibrous reinforcement, which virtually prevents making thin-wall articles from fibrous concrete. In addition, molding articles by this apparatus requires excesive consumption of the initial mix ingredients (such as cement and fibre), thus rendering the end product less cost-effective.